Method of making a gun barrel



June 27, 1961 G. c. SULLIVAN METHOD OF MAKING A GUN BARREL Original Filed Feb. 19. 1952 2 Sheets-Sheet 1 INVENTOR June 27, 1961 G. c. SULLIVAN METHOD OF MAKING A GUN BARREL Original Filed Feb. 19, 1952 2 Sheets-Sheet 2 mm 3 mm on n m n m SJ m G O 1 Oh" United States Patent C i Original application Feb. 19, 1952, Ser. No. 272,428, now

Patent No. 2,780,019, dated Feb. 5, 1957. Divided and this application, Aug. 17, 1954, Ser. No. 450,442

2 Claims. (Cl. 204-26) This invention relates to a firearm or more particularly to a barrel construction wherein the design and materials employed are of such a nature that the resultant product is a minimum in weight. This is accomplished in such a manner that other factors necessary in a practical and successful gun barrel, such as strength and life, are not jeopardized.

The present invention provides a firearm barrel made of a light-Weight non-ferrous alloy, preferably aluminum, and including a bore having a plated or hard-coated internal surface. The present application is a division of my copending application Serial No. 272,428, filed Feb. ruary 19, 1952, now Patent No. 2,780,019.

The present invention also provides a method of making a firearm barrel, or the like, comprising the steps of machining the barrel from an aluminum alloy blank, drilling a bore axially of the blank, the bore having a diameter slightly in excess of the required finished diameter, and hard-coating the surface of the bore to a dimension at least that required for finished bore diameter. In the case of firearms having low breech pressures, the alloy blank itself may be originally formed in a tubular shape by the use of various 'well known techniques, thus integrally containing a bore which can be finished as described hereinafter.

Sportsmen, as well as ordnance manufacturers, have made many attempts to reduce the weight in firearms, for it is recognized that such a light-weight firearm would be advantageous in many respects. Both the sportsmen and the soldier will be less fatigued at the end of the day if he has carried less weight. Elforts have been made in the past to decrease action or receiver, stock and sights weight but little, any, has been attained in reducing barrel weight. This invention discloses a construction and method of manufacture of a gun barrel of reduced weight, yet is of sufficient material cross-section to minimize barrel whip.

As the weight of a firearm is reduced, the recoil normally increases. While it has been found that the increase in recoil is not fatiguing to the average shooter, it may be found desirable to provide a recoil minimizing device. This invention is particularly advantageous in that the decreased weight of the basic material in the barrel will allow a larger barrel cross-section which decreases barrel whip and therefore increases shooting accuracy. This larger barrel cross-section can be carried to the muzzle, thus permitting the use of a muzzle brake or blast device which can be designed into and form a part of the barrel itself. This feature permits a construction that is streamlined, pleasing to the eye in comparison to present devices, economical of manufacture and light in weight. The reduced weight of the basic material used in this invention also allows (for a longer barrel which is advantageous in the event of a military weapon and its accompanying bayonet.

Among the objects achieved in the present invention are the provision of a gun barrel construction in which a non-ferrous alloy is used in conjunction with a hardplated barrel or bore; a sleeve or liner being incorporated near the chamber of the barrel if desired. The preferred alloy is comprised essentially of aluminum combined with one or more group metals such as zinc, magnesium and copper. For instance, a material discovered to be Patented June 27, 1961 practical and workable in this application has the following constituents; aluminum 88.5%, magnesium 2.5%, zinc 5.5%, copper 1.5%, chromium 0.30%; the remainder consisting of impurities. Obviously, these metals, can be varied within reasonable limits without the resultant material being affected. A preferred material of this type is a wrought alloy which has received solution heat treatment and elevated temperature aging, and is formed by rolling or preferably by extrusion processes. An alternate aluminum alloy material which may be preferred later is one in which the amount of alloying metals, notably magnesium and zinc, has been increased over that disclosed above. This material is stronger in that the ultimate tensile strengths have been increased approximately 8% to date, such material being somewhat experimental in nature at the present time. Tensile strengths as much as 100,000 pounds per square inch and yield strengths of 95,000 pounds per square inch are obtainable.

These materials are particularly advantageous in they are not only light in weight (.10 pound/ cubic inch versus .28 pound/cubic inch) when compared to high-strength steels, but have greater thermal conductivity factors (.30 versus .10); the latter fact being of value in the minimization of firing temperatures. This material in combination with cooling fins which may be extruded originally or machined later about the chamber area, will provide excellent cooling of the barrel.

I have found that a barrel of the above mentioned material will not withstand repeated firing unless a hardplating is applied to its internal bore. To that end, I propose the use of a chromium or a hard anodic, or the like, plating. For instance, a typical method of chromium plating would be to insert an anode or cathode bar through the bore of the barrel and immerse the combination in an electrolyte for the plating operation; all in accordance with well-known current procedure. The barrel can be anodized first and then ground to remove the oxide below the area to be plated. It may be desirable to give the barrel a flash of copper or nickel to seal the alloy material from water penetration causing corrosion and to prepare a better bonding surface for the chromium plate. The plating is then applied by standard methods. It has been found wise to rotate the barrel during the plating operation to minimize the possibility of uneven plating thickness.

Effort is made to control the thickness of the plating in order to eliminate subsequent machine operations; however, it is to be understood that the plating can be increased and later reduced to finish dimensions by polishing, grinding, reaming, lapping, honing, or the like, machine or hand operations.

Another type of hard-coating has been applied to the bore with great success, such coating being applied by an electro-chemical process which creates a non-metallic, hard, heat and corrosion resistant surface which is integral with the base material, not usually requiring the use of a separate plating metal, as described above. One type coating can be created by passing a current through an oxidizing solution, the time of operation and intensity of current determining principally the thickness of the coating obtained, such coating being termed as surface oxidation. A coating of this type will provide a hard, practical coating for the gun barrel of this invention; such coating having been found to be excellent in that it produces an anodized coating having a hard, dense and corrosion resistant surface. These coatings, usually being composed of amorphous alumina (A1 0 offer very good resistance to wear and abrasion, and are valuable in that it is highly refractory in nature, offering resistance to high temperatures.

A coating treatment which has resulted in a fine product consists of an electrolytic bath containing principally sulphuric acid, the preferred temperature of which has been lowered to approximately 30 to 32 F. Slightly higher temperatures (up to 55 F.) may be used satisfactorily but with less advantage. The use of carbon dioxide as a temperature reducing medium has been found to be excellent in that the carbon dioxide not only performs a refrigerating function but enters into the reaction in such a way that the resultant composition of coating has extremely good resistance to wear. Oxalic acid can be added to the bath solution thus permitting higher bath temperatures and resultant lowered costs of operation, but the coating may suffer some in physical characteristics.

The hard coating type of process, distinguishable from the plating process in that the hard coating is formed from the basic material of the barrel itself instead of depositing a plating of another material on the barrel, is advantageous in that there is a surface impregnation which renders a highly efficient joint action between the hard coating and the basic material of the barrel. In this process a dimensional growth may be associated with the formation of the hard oxide films, and this feature should be taken into consideration in the design of the barrel. The oxide surface, although extremely hard, can be finished by honing, lapping, or the like, methods to produce very smooth surfaces.

A gun barrel when treated according to the process above described has excellent resistance to corrosion and erosion and if designed with taper its performance can be substantially improved.

With the above and other objects in view, those skilled in the art will appreciate the advantages and the invention as disclosed herein, after reviewing the accompanying drawings wherein:

FIGURE 1 is a side view of a typical barrel incorporating the present invention, part of FIGURE 1 being shown in an enlarged and cross-sectioned manner;

FIGURE 2 is a cross-sectional view of the barrel showing details of the present invention including the provision for a sleeve or liner;

FIGURE 3 is a sectional view of the barrel showing the plating or coating applied to the bore;

FIGURE 4 is an elevational cross-sectioned view of the chamber portion of the barrel, showing an alternate liner;

FIGURE 5 is a. sectional view of the barrel showing said alternate liner;

FIGURE 6 is a sectional view of the muzzle end of the barrel showing an integral recoil minimizing device;

FIGURE 7 is a sectional view of an alternate design of barrel in which the chamber is incorporated in a liner, cooling fins provided about the chamber area, and the bore being so processed that it is provided with a tapered internal diameter; and

FIGURE 8 shows a general method of hard plating the barrel and obtaining a tapered bore if desired.

As shown in the drawings, the composite barrel of the present invention includes a barrel body 10 formed of a light-weight material such as aluminum alloy, having the usual bore 11 which may be rifled in the usual manner to provide interior helical-like lands 12 and grooves 13. The barrel 10 is provided at its rear end with an externally threaded shank 14 or other typical means by which the barrel may be attached to the action or receiver.

The barrel 10, and particularly the bore 11 is coated with a hard coating 1'5. While it is essential in this invention to coat or plate the bore 11, it is not necessary, however, it may be desirable, to apply a coating to the outside surface of the barrel 10, such coating being accomplished in accordance with procedures outlined herein. The hard coating or plating 15 may be applied to the chamber 16 to assist in preventing erosion therein, however, it may be preferred to block off or mask both the chamber 16 and the threads 14 from this operation by using a vinyl tape, or the like, thus preventing interference with prior machining to close tolerances and headspacing of the barrel and action. The barrel can, if desired, be substantially machine finished prior to plating or coating, leaving .001 to .004 inch or less tolerance for the thickness of the coating to be applied.

The rear end of the barrel 10 contains the usual chamber 16, the size and shape of which is determined by the cartridge and caliber used. The explosion pressures are a maximum in the area of the chamber 16 and reduce in the direction of the muzzle 17. While available lightweight metals have been found to have suificient strength to withstand with safety the explosion pressures encountered, it may be advisable, if a barrel of exceedingly lowweight is wanted, to incorporate a sleeve 18 around the chamber 16 area where pressures are at a maximum. An alternate sleeve or liner 19 may be incorporated adjacent the chamber 16; this type of strengthening element having the additional advantage of being removable and replaceable in event of excessive erosion due to repeated firing. Both the sleeve 18 and the liner 19 may be installed by sweating the parts together or by furnace brazing, or the like. In the first case, the heat produced as a result of firing tends to increase joint efiiciency action and thus permit each element to absorb its proportion of the stresses produced. The sleeve 18 can drop into detents 20 for security and the liner 19 can be secured by conventional means, such as threading, and the like.

The sleeve 18 or liner '19 is preferably made of a highstrength metal such as stainless steel, which has a tensile strength approaching 125,000 pounds per square inch, or a titanium alloy having a tensile strength in excess of 150,000 pounds per square inch; the latter having the additional advantage of light-weight. A typical material of the latter type is a titanium alloy containing approximately 5% chromium and 3% aluminum. Currently used high strength ordnance steels may also be used.

The muzzle 17 can, if desired, be constructed with a recoil absorbing device as disclosed in FIGURE 6. The blast chamber 21 can be formed in several Ways, by undercutting from the muzzle end of the barrel or by drilling a hole 22 and inserting a plug 23 therein; the plug 23 having an inside diameter slightly greater than the groove diameter of the bore 11 and being attached by conventional means such as threading 24, and the like. Blast holes 25 are drilled through the barrel 11 to provide gas exit and recoil absorption. FIGURE 6 shows the plating or hard coating 15 being applied not only to the bore 11 but also to the outside of the barrel.

The method of manufacture as disclosed by this invention is particularly advantageous in that it lends itself well to the production of a barrel having a tapered bore if so desired, such a tapered bore being obtained in a very economical manner when compared with other fabrication processes. In the alternate design of FIGURE 7, a barrel 26 incorporates a liner 27 constructed of a high strength material. The barrel 26 includes fins 28 about the chamber area for cooling purposes. The liner 27 can be attached to the barrel 26 by conventional means; the attachment shown in FIGURE 7 including a series of splines 29 to insure proper alignment of the riflings 30 and 31 at the joint 32. The liner 27 is firmly attached to the remaining portion of the barrel by means of threads 33 and coupling 34. It is to be understood that the liner 27 can be secured to the barrel proper by direct threading therebetween or by other means. FIGURE 7 shows, in an exaggerated manner, a plating or hard coating 35 which is comparatively thin adjacent the chamber of the barrel and which gradually increases in thickness as the muzzle is approached. This tapering effect is advantageous in that the accuracy of the barrel is improved considerably, while permitting the lowering of critical breech pressures. Tapered rifling is also of advantage in that with such a construction a bullet jacket can be fabricated of a harder material, thus allowing greater penetrating power.

The taper of the barrel bore is obtained as a result of the hard coating process, as shown by FIGURE 8. For example, the barrel 26, having a constant bore diameter as a result of machining procedures, is placed within a tank 36 which contains an electrolytic solution 37, as hereinbefore described. The barrel 26 is preferably inserted about a cathode rod 38 which may be of a material such as lead or coated stainless steel and the like and which may be negatively charged and spaced therefrom by appropriate techniques and means now employed in the plating industry. The barrel 26 may be positively charged to an anode in such a manner that a current flows through the electrolyte 37 to accomplish the formation of the hard coating 35.

Inasmuch as the formation of the coating is primarily a function of time of immersion, temperature of electrolyte and intensity or density of current applied, it will be seen that by controlling these factors a tapered coating can be easily obtained. For instance the barrel can be wholly inserted into the electrolyte and gradually raised or taken out of the bath, by appropriate facilities such as a lifting means 39, thus producing a bore which may be tapered uniformly or non-uniformly in either direction in accordance with the most desired design of barrel. It may be found desirable to always keep the barrel in the electrolyte during the taper processing cycle in which event other Well-known techniques can be used. Of course, if no taper is desired, the barrel will be treated uniformly over its whole length. After treatment the barrel is preferably transferred to a cold water rinse to remove any residual electrolyte.

While a rifle barrel has been chosen for illustration and description, it will be understood that the invention is equally applicable to machine guns, shot guns or small arms barrels, such as revolvers or automatics. It may be also applied to other type of firearms or ordnance Where reduced weight is desirable, such as mobile field or tank guns, infantry mortars, recoilless rifles and the like. Smooth bore firearms are Well adaptable to this process of manufacture.

It should be apparent that numerous modifications may be made without departing from the spirit of the invention as expressed in the claims.

I claim:

1. The method of making a gun barrel, comprising the fabrication of said barrel from an aluminum alloy blank, electrochemically treating substantially the complete barrel in a bath composed principally of sulphuric acid in which the barrel is the anode and at a refrigerated temperature, and controlling treatment factors such as time of immersion on successive increments of the barrel to produce a tapered hard coated surface.

2. The method of making a gun barrel, comprising the general steps of machining said barrel from an aluminum alloy blank, providing a chamber and a bore axially of the blank, inserting said barrel into an electrolytic bath, and gradually raising said barrel from said bath while passing a current through said bath, whereby said bore is coated throughout its length with a coating formed from the base material and at a controlled growth to effect a tapered bore.

References Cited in the file of this patent UNITED STATES PATENTS 1,441,468 Wills Jan. 9, 1923 1,886,218 Olin Nov. 1, 1932 2,036,740 Bengston Apr. 7, 1936 2,413,022 Woody Dec. 24, 1946 2,425,359 Zavarella Aug. 12, 1947 2,736,118 Clarkson et al. Feb. 28, 1956 FOREIGN PATENTS 831,030 France May 30, 1938 4,095 Switzerland Sept. 28, 1891 OTHER REFERENCES Mason et al.: Metal Finishing, February 1948, pp. -70.

Miyata: Transactions of the Chemical Engineering Congress of the World Power Conference, London, 1936, vol. 2, pp. 569-584. 

2. THE METHOD OF MAKING A GUN BARREL, COMPRISING THE GENERAL STEPS OF MACHINING SAID BARREL FROM AN ALUMINUM ALLOY BLANK, PROVIDING A CHAMBER AND A BORE AXIALLY OF THE BLANK, INSERTING SAID BARREL INTO AN ELECTROLYTIC BATH, AND GRADUALLY RAISING SAID BARREL FROM SAID BATH WHILE PASSING A CURRENT THROUGH SAID BATH, WHEREBY SAID 